Placement of the mitotic spindle is crucial for the proper inheritance of segregated cytoplasmic determinants to daughter cells. Cell cleavage planes are determined by the position of the centrosomes of the mitotic spindle. A cleavage plane will form between the two centrosomes, thus partitioning cytoplasmic components to particular cells. Work done by Bob Goldstein (1995), in C. elegans showed that cleavage in certain cell divisions can be specified by cell contact mediated events. This contact appears to induce a site in the cortex that attracts a centrosome, resulting in nuclear/centrosome rotation and consequent alignment of the spindle. We are investigating the cytoskeletal rearrangements that occur upon cell contact between neighboring cells in C. elegans; specifically the interaction between P2 and EMS blastomeres isolated in vitro. The P2 blastomere appears to align tbe mitotic spindle in EMS via contact, such that specific cytoplasmic determinants are partitioned to one of the daughter cells of EMS. Ultimately, we would like to understand the interaction between the P2 and EMS blastomeres spatially and temporally, as well as, the nature of the cortical site and factors involved in the alignment of the spindle. We plan to use a combination of confocal and immuno-electron microscopy to visualize cytoskeletal components that are associated with the attachment site. Goldstein, B. (1995). J.Cell Biology, 129:1071-1080.